Method for capturing mr image data and corresponding combined mr/et facility

ABSTRACT

MR image data relating to a volume section of an examination object is determined. Image data relating to this volume section is also captured by way of a true-to-original tomographic method. The MR image data is compared with the image data. Depending on the results of this comparison, either the MR image data is corrected such that the MR image data matches the image data as closely as possible, or parameters that are used during the capture of the MR image data are modified such that, when the MR image data of the predefined volume section is captured again using the modified parameters, the newly captured MR image data matches the image data as closely as possible.

PRIORITY STATEMENT

The present application hereby claims priority under 35 U.S.C. §119 toGerman patent application number DE 10 2011 007 871.1 filed Apr. 21,2011, the entire contents of which are hereby incorporated herein byreference.

FIELD

At least one embodiment of the present invention generally relates tothe capture of MR image data with reference to image data that has beencaptured by way of a true-to-original tomographic method, and/or acombined MR/ET facility that has been configured correspondingly.

BACKGROUND

It is known that MR images do not constitute a geometrically accuraterepresentation. Due to the assignment of the raw data that is capturedin the frequency space (k-space) to the location space, due to incorrectdeviations in the gradient linearity and due to the inhomogeneity of thebasic magnetic field, the MR images are usually distorted because amagnetic resonance installation measures frequencies in the MHz rangeand does not measure geometric information. Depending on the sequencetechnique, this results in MR images providing more or less inaccurategeometric representations, echo planar imaging (EPI) in particular beingone of the sequence techniques that react particularly sensitively tothe effects described above.

SUMMARY

At least one embodiment of the present invention improves the geometricrepresentational accuracy of MR images (i.e. the accuracy with which theMR images depict geometric realities in the volume section that isdepicted) relative to the prior art.

According to at least one embodiment of the invention, a method forcapturing MR image data is disclosed; a combined MR/ET facility isdisclosed; a computer program product is disclosed and an electronicallyreadable data medium is disclosed. The dependent claims define preferredand advantageous embodiments of the present invention.

In the context of at least one embodiment of the present invention, amethod is provided for capturing MR image data by WAY of a magneticresonance installation. This method comprises:

capturing the MR image data relating to a predefined volume section ofan examination object (e.g. a patient) by means of the magneticresonance installation;

capturing image data of the predefined volume section by means of atrue-to-original tomographic method;

comparing the MR image data with the image data; and

correcting the MR image data depending on the results of the comparison,such that the MR image data matches the image data as closely aspossible.

In the context of at least one embodiment of the present invention, afurther method is provided for capturing MR image data by way of amagnetic resonance installation. This further inventive methodcomprises:

capturing MR image data relating to a predefined volume section of anexamination object (e.g. a patient) by means of the magnetic resonanceinstallation, specific parameters being used during the capture of theMR image data (this comprising in particular a capture of MR raw dataand a reconstruction of the MR image data from this MR raw data);

capturing image data of the predefined volume section by means of atrue-to-original tomographic method;

comparing the MR image data with the image data;

modifying the parameters depending on the results of the comparison,such that when the MR image data of the predefined volume section iscaptured again, using the modified parameters in this case, the newlycaptured MR image data matches the image data as closely as possible;and

capturing the MR image data of the predefined volume section again,using the modified parameters.

In the context of at least one embodiment of the present invention,provision is also made for a combined MR/ET facility for capturing MRimage data of a predefined volume section of an examination object. Inthis case, the MR/ET facility comprises a control unit for activating anemission detector of the MR facility and a magnetic resonanceinstallation of the MR facility, and an image computing unit forreceiving raw data of the predefined volume section, said raw datahaving been captured by the emission detector, and receiving MR raw dataof the predefined volume section, said MR raw data having been recordedby the magnetic resonance installation, and for creating the MR imagedata from the MR raw data and image data from the raw data. In thiscase, the emission detector is so configured as to capturetrue-to-original tomographic raw data. The MR/ET facility is soconfigured as to compare the MR image data with the image data and tocorrect the MR image data depending on the results of this comparison,such that the MR image data matches the image data as closely aspossible.

At least one embodiment of the present invention also describes acomputer program product, in particular a computer program or software,which can be loaded into a memory of a programmable control or acomputer unit of a combined MR/ET facility. Using the computer programproduct, all or various of the above-described embodiments of theinventive method can be executed when the computer program product runsin the control or control unit of the combined MR/ET facility. In thiscase, the computer program product might require programming resourcessuch as libraries and help functions, for example, in order to realizethe corresponding embodiments of the methods. In other words, the claimrelating to the computer program product is intended to include in thescope of protection in particular a computer program or software bymeans of which one of the above described embodiments of the inventivemethods can be executed and/or which executes said embodiment. In thiscase, the software can be a source code (e.g. C++) which remains to becompiled (translated) and linked or which merely needs to beinterpreted, or an executable software code which merely needs to beloaded into the relevant computer unit for execution.

Lastly, at least one embodiment of the present invention discloses anelectronically readable data medium, e.g. a DVD, a magnetic tape or aUSB stick, on which is stored electronically readable controlinformation, in particular software (see above). When this controlinformation (software) is read from the data medium and stored in acontrol or computer unit of a combined MR/ET facility, all of theinventive embodiments of the above described methods can be performed.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in detail below on the basis ofexample embodiments according to the invention and with reference to thefigures, in which:

FIG. 1 schematically illustrates a combined MR/PET facility according toan embodiment of the invention,

FIG. 2 illustrates a flow diagram of a first method according to anembodiment of the invention, and

FIG. 3 illustrates a flow diagram of a second method according to anembodiment of the invention.

It should be noted that these Figures are intended to illustrate thegeneral characteristics of methods, structure and/or materials utilizedin certain example embodiments and to supplement the written descriptionprovided below. These drawings are not, however, to scale and may notprecisely reflect the precise structural or performance characteristicsof any given embodiment, and should not be interpreted as defining orlimiting the range of values or properties encompassed by exampleembodiments. The use of similar or identical reference numbers in thevarious drawings is intended to indicate the presence of a similar oridentical element or feature.

DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS

Various example embodiments will now be described more fully withreference to the accompanying drawings in which only some exampleembodiments are shown. Specific structural and functional detailsdisclosed herein are merely representative for purposes of describingexample embodiments. The present invention, however, may be embodied inmany alternate forms and should not be construed as limited to only theexample embodiments set forth herein.

Accordingly, while example embodiments of the invention are capable ofvarious modifications and alternative forms, embodiments thereof areshown by way of example in the drawings and will herein be described indetail. It should be understood, however, that there is no intent tolimit example embodiments of the present invention to the particularforms disclosed. On the contrary, example embodiments are to cover allmodifications, equivalents, and alternatives falling within the scope ofthe invention. Like numbers refer to like elements throughout thedescription of the figures.

Before discussing example embodiments in more detail, it is noted thatsome example embodiments are described as processes or methods depictedas flowcharts. Although the flowcharts describe the operations assequential processes, many of the operations may be performed inparallel, concurrently or simultaneously. In addition, the order ofoperations may be re-arranged. The processes may be terminated whentheir operations are completed, but may also have additional steps notincluded in the figure. The processes may correspond to methods,functions, procedures, subroutines, subprograms, etc.

Methods discussed below, some of which are illustrated by the flowcharts, may be implemented by hardware, software, firmware, middleware,microcode, hardware description languages, or any combination thereof.When implemented in software, firmware, middleware or microcode, theprogram code or code segments to perform the necessary tasks will bestored in a machine or computer readable medium such as a storage mediumor non-transitory computer readable medium. A processor(s) will performthe necessary tasks.

Specific structural and functional details disclosed herein are merelyrepresentative for purposes of describing example embodiments of thepresent invention. This invention may, however, be embodied in manyalternate forms and should not be construed as limited to only theembodiments set forth herein.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of example embodiments of thepresent invention. As used herein, the term “and/or,” includes any andall combinations of one or more of the associated listed items.

It will be understood that when an element is referred to as being“connected,” or “coupled,” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected,” or “directly coupled,” to another element, there are nointervening elements present. Other words used to describe therelationship between elements should be interpreted in a like fashion(e.g., “between,” versus “directly between,” “adjacent,” versus“directly adjacent,” etc.).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments of the invention. As used herein, the singular forms “a,”“an,” and “the,” are intended to include the plural forms as well,unless the context clearly indicates otherwise. As used herein, theterms “and/or” and “at least one of” include any and all combinations ofone or more of the associated listed items. It will be furtherunderstood that the terms “comprises,” “comprising,” “includes,” and/or“including,” when used herein, specify the presence of stated features,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof.

It should also be noted that in some alternative implementations, thefunctions/acts noted may occur out of the order noted in the figures.For example, two figures shown in succession may in fact be executedsubstantially concurrently or may sometimes be executed in the reverseorder, depending upon the functionality/acts involved.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which example embodiments belong. Itwill be further understood that terms, e.g., those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

Portions of the example embodiments and corresponding detaileddescription may be presented in terms of software, or algorithms andsymbolic representations of operation on data bits within a computermemory. These descriptions and representations are the ones by whichthose of ordinary skill in the art effectively convey the substance oftheir work to others of ordinary skill in the art. An algorithm, as theterm is used here, and as it is used generally, is conceived to be aself-consistent sequence of steps leading to a desired result. The stepsare those requiring physical manipulations of physical quantities.Usually, though not necessarily, these quantities take the form ofoptical, electrical, or magnetic signals capable of being stored,transferred, combined, compared, and otherwise manipulated. It hasproven convenient at times, principally for reasons of common usage, torefer to these signals as bits, values, elements, symbols, characters,terms, numbers, or the like.

In the following description, illustrative embodiments may be describedwith reference to acts and symbolic representations of operations (e.g.,in the form of flowcharts) that may be implemented as program modules orfunctional processes include routines, programs, objects, components,data structures, etc., that perform particular tasks or implementparticular abstract data types and may be implemented using existinghardware at existing network elements. Such existing hardware mayinclude one or more Central Processing Units (CPUs), digital signalprocessors (DSPs), application-specific-integrated-circuits, fieldprogrammable gate arrays (FPGAs) computers or the like.

Note also that the software implemented aspects of the exampleembodiments may be typically encoded on some form of program storagemedium or implemented over some type of transmission medium. The programstorage medium (e.g., non-transitory storage medium) may be magnetic(e.g., a floppy disk or a hard drive) or optical (e.g., a compact diskread only memory, or “CD ROM”), and may be read only or random access.Similarly, the transmission medium may be twisted wire pairs, coaxialcable, optical fiber, or some other suitable transmission medium knownto the art. The example embodiments not limited by these aspects of anygiven implementation.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise, or as is apparent from the discussion,terms such as “processing” or “computing” or “calculating” or“determining” of “displaying” or the like, refer to the action andprocesses of a computer system, or similar electronic computingdevice/hardware, that manipulates and transforms data represented asphysical, electronic quantities within the computer system's registersand memories into other data similarly represented as physicalquantities within the computer system memories or registers or othersuch information storage, transmission or display devices.

Spatially relative terms, such as “beneath”, “below”, “lower”, “above”,“upper”, and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, term such as “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein are interpreted accordingly.

Although the terms first, second, etc. may be used herein to describevarious elements, components, regions, layers and/or sections, it shouldbe understood that these elements, components, regions, layers and/orsections should not be limited by these terms. These terms are used onlyto distinguish one element, component, region, layer, or section fromanother region, layer, or section. Thus, a first element, component,region, layer, or section discussed below could be termed a secondelement, component, region, layer, or section without departing from theteachings of the present invention.

In the context of at least one embodiment of the present invention, amethod is provided for capturing MR image data by WAY of a magneticresonance installation. This method comprises:

capturing the MR image data relating to a predefined volume section ofan examination object (e.g. a patient) by means of the magneticresonance installation;

capturing image data of the predefined volume section by means of atrue-to-original tomographic method;

comparing the MR image data with the image data; and

correcting the MR image data depending on the results of the comparison,such that the MR image data matches the image data as closely aspossible.

In the context of at least one embodiment of the present invention, atomographic method is understood to be an imaging method whichdetermines the internal spatial structure of an object and depicts it inthe form of an image (e.g. a sectional image). True-to-original meansthat geometric structures may be enlarged or reduced, rotated and/ormirrored in their entirety, but may not be represented or depicted in adistorted manner, and therefore length ratios and angles of the spatialstructure are preserved in the image. Depending on the tomographicmethod, true-to-original can also signify length-preserving andangle-preserving in an absolute sense. If the tomographic method depictsthe spatial structures in a length-preserving manner, a volume of thespatial structure that is to be represented can be represented (andtherefore measured) precisely.

In the context of embodiments of the invention, comparing the MR imagedata and the image data is understood to comprise an examination of howthe MR image data can be migrated or transformed into the image data.Such a procedure is known from the registration of two images. In thiscase, the registration is a method or a process for reconciling to thegreatest possible extent one image (the MR image in the present case)with another image (the image created by the true-to-originaltopographical method in this case). To this end, provision is usuallymade for calculating a transformation by which the MR image or the MRimage data is adapted as optimally as possible to the image or the imagedata. Unlike the registration, the comparison does not perform theregistration, but merely determines corresponding data or information.

The correction of the MR image data depending on the results of thecomparison can be performed, for example, so as to execute aregistration of the MR image data with the image data, the results ofthe comparison therefore being used in order to adapt the MR image dataas optimally as possible to the image data.

As a result of the MR image data being corrected by way of the imagedata as per the invention, the MR image data has improved locationintegrity or geometric accuracy after this correction. Furthermore, thecorrection of the MR image data results in an improved correspondence ofthe image points of the MR image data to the corresponding image pointsof the image data, this being particularly advantageous with regard to afusion of the MR image data and the image data.

In the context of at least one embodiment of the present invention, afurther method is provided for capturing MR image data by way of amagnetic resonance installation. This further inventive methodcomprises:

capturing MR image data relating to a predefined volume section of anexamination object (e.g. a patient) by means of the magnetic resonanceinstallation, specific parameters being used during the capture of theMR image data (this comprising in particular a capture of MR raw dataand a reconstruction of the MR image data from this MR raw data);

capturing image data of the predefined volume section by means of atrue-to-original tomographic method;

comparing the MR image data with the image data;

modifying the parameters depending on the results of the comparison,such that when the MR image data of the predefined volume section iscaptured again, using the modified parameters in this case, the newlycaptured MR image data matches the image data as closely as possible;and

capturing the MR image data of the predefined volume section again,using the modified parameters.

In the context of at least one embodiment of this further inventivemethod, the MR image data that is recorded using the modified parameterslikewise has better geometric accuracy than is the case in the prior art(without modification of the parameters). This again results in a bettermatch between the image points of the MR image data and thecorresponding image points of the image data.

While the correction of the MR image data according to at least oneembodiment of the inventive method is done in a quasi image-basedmanner, i.e. after a corresponding reconstruction of the raw data toproduce the MR image data, the further inventive method involves amodification of parameters which can also be used during thereconstruction of the MR image data from the MR raw data, for example.

In the context of at least one embodiment of the further inventivemethod, it is possible to apply a warp correction, for example, whereinthe parameters to be specified are parameters of said warp correction.These parameters are modified depending on the results of the comparisonin such a way that the MR image data, which has been corrected withreference to the warp correction that is based on the correspondinglymodified parameters, matches the image data as closely as possible.

In this case, a warp correction is understood to be any correction bywhich effects that negatively influence the geometric representationalaccuracy of the MR image data are at least moderated.

As indicated above, MR raw data can be captured in advance (e.g. bysampling the k-space) for the purpose of capturing the MR image. The MRimage data is reconstructed from the MR raw data in this case, whereinthe cited parameters are applied. Depending on the results of thecomparison, these parameters are modified such that when the MR imagedata is reconstructed from the MR raw data again, using the modifiedparameters, the newly reconstructed MR image data matches the image dataas closely as possible.

The parameters that are used can be correction parameters for correctingan MR distortion. The parameters for modeling and/or correcting gradientnon-linearities or undesired basic field effects can be used in thiscase. In other words, provision is inventively made for the correctionparameters to be specified and then applied to a prospective correctionof MR distortions.

In particular, the specification of the parameters takes the form of acalibration measurement, which can advantageously be performed on thepatient concerned.

Using the parameters that are applied for the reconstruction of the MRimage data from the MR raw data, it is also possible e.g. to perform acorrection of the MR raw data, this normally being captured as complexnumbers (e.g. amplitude and phase). For example, these parameters cancomprise a phase difference which is used to correct the phase of the MRraw data that is captured when sampling the k-space.

For the purpose of setting or specifying the parameters, a targetfunction that is used to determine an image similarity between the MRimage data and the image data can be defined, for example. Theparameters are then modified in a type of control loop or iterationuntil the reconstruction of the MR image data by way of the parametersresults in an optimum of the target function.

If the parameters include the phase difference, the invention offers twovariants in relation to this phase difference:

1. The phase difference applies globally, i.e. the same phase differenceis used for all MR raw data (for all k-space points).

2. A phase difference is used and specified individually for eachk-space point. This second variant also comprises subvariants. Forexample, the same phase difference can be used for all k-space points ofthe same k-space row or k-space column. Or the same phase difference isused for those k-space points which have a predefined proximityrelationship in the k-space.

In other words, only one parameter need be specified in the case of thefirst variant, namely the phase difference that is globally applied. Inthe case of the second variant, however, a dedicated phase differencemust be specified for each k-space point or for a plurality of k-spacepoints (which have a specific proximity relationship in the k-space).With regard to the second variant, use is made of smoothing inparticular to ensure that the difference between the phase differencesof two adjacent k-space points is no greater than a predefined thresholdvalue.

According to at least one embodiment of the invention, the comparison ofthe MR image data with the image data involves examining how the MRimage data can be migrated into the image data using a non-rigidregistration, wherein this applies to both the inventive method and thefurther inventive method. In this case, a rigid registration isunderstood to be a registration in which the same shift vector (i.e. oneshift vector only) for all image points is specified for each imagepoint of the MR image. In the case of non-rigid or elastic registration,however, each image point of the MR image has a dedicated shift vectorwhich is used to shift the corresponding image point in such a way thatthe MR image as closely as possible matches the image that was createdby the true-to-original tomographic method.

In both embodiments of the inventive method and the further inventivemethod, those methods in which radiation is measured can be used as atrue-to-original tomographic method. In this case, a distinction is madebetween methods in which said radiation is generated outside of thevolume section that is to be represented, e.g. x-ray methods, andmethods in which the radiation to be captured is generated inside thevolume section that is to be represented (e.g. by injection ofradioactive tracers), wherein this is known as emission computertomography and includes e.g. PET (“positron emission tomography”) andSPECT (“single photon emission computed tomography”).

In both embodiments of the inventive method and the further inventivemethod, the MR image data and the image data are advantageously capturedsimultaneously.

The simultaneous capture of the MR image data and the image data ispossible firstly because the magnetic resonance installation isindependent of the true-to-original tomographic method. Secondly, thesimultaneous capture of the MR image data and the image data has theadvantage that there are no differences between the MR image data andthe image data due to object movements which could occur if the MR imagedata and the image data were created at different time points.

The comparison of the MR image data with the image data can be done byway of anatomical features of the examination object (e.g. following atracer injection), wherein these anatomical features must be visible inboth the MR image data and the image data of the true-to-originaltomographic method (e.g. must be present in the field of view in eachcase). The comparison can also be effected by way of markers (e.g.pellets that are filled with a tracer and are also visible in the MRimages), wherein the markers here must again be present in the field ofview of both methods (MR method and true-to-original tomographicmethod).

In the context of at least one embodiment of the present invention,provision is also made for a combined MR/ET facility for capturing MRimage data of a predefined volume section of an examination object. Inthis case, the MR/ET facility comprises a control unit for activating anemission detector of the MR facility and a magnetic resonanceinstallation of the MR facility, and an image computing unit forreceiving raw data of the predefined volume section, said raw datahaving been captured by the emission detector, and receiving MR raw dataof the predefined volume section, said MR raw data having been recordedby the magnetic resonance installation, and for creating the MR imagedata from the MR raw data and image data from the raw data. In thiscase, the emission detector is so configured as to capturetrue-to-original tomographic raw data. The MR/ET facility is soconfigured as to compare the MR image data with the image data and tocorrect the MR image data depending on the results of this comparison,such that the MR image data matches the image data as closely aspossible.

In the context of at least one embodiment of the present invention,provision is also made for a further combined MR/ET facility forcapturing MR image data of a predefined volume section of an examinationobject. In this case, the MR/ET facility comprises a control unit foractivating an emission detector of the MR/ET facility and a magneticresonance installation of the MR/ET facility, and an image computingunit for receiving raw data of the predefined volume section, said rawdata having been captured by the emission detector, and receiving MR rawdata of the predefined volume section, said MR raw data having beenrecorded by the magnetic resonance installation, and for creating the MRimage data from the MR raw data, depending on parameters, and creatingimage data from the raw data. In this case, the emission detector is soconfigured as to capture true-to-original tomographic raw data. TheMR/ET facility is so configured as to set or modify the parametersdepending on results of a comparison between the MR image data and theimage data such that, after the MR image data has been created from theMR raw data again (using the modified parameters), the newly created MRimage data matches the image data as closely as possible.

According to at least one embodiment of the invention, a combined MR/ETfacility is understood in this case to be a facility that comprises acombination of a magnetic resonance tomograph and an emission computertomograph (e.g. a positron emission tomograph) or an x-ray system. Inother words, a combined MR/ET facility is understood to be a facilitywhich, in addition to a magnetic resonance tomograph, comprises aninstallation that can perform a true-to-original tomographic method (seeabove). Such an installation can therefore also be an installation thatitself generates the radiation by means of which the volume section isirradiated and represented, as is the case when using an x-ray system,for example.

In this case, the advantages of the inventive combined MR/ET facilitiescorrespond essentially to the advantages of the inventive method, whichare explained in detail above and are therefore not repeated here.

At least one embodiment of the present invention also describes acomputer program product, in particular a computer program or software,which can be loaded into a memory of a programmable control or acomputer unit of a combined MR/ET facility. Using the computer programproduct, all or various of the above-described embodiments of theinventive method can be executed when the computer program product runsin the control or control unit of the combined MR/ET facility. In thiscase, the computer program product might require programming resourcessuch as libraries and help functions, for example, in order to realizethe corresponding embodiments of the methods. In other words, the claimrelating to the computer program product is intended to include in thescope of protection in particular a computer program or software bymeans of which one of the above described embodiments of the inventivemethods can be executed and/or which executes said embodiment. In thiscase, the software can be a source code (e.g. C++) which remains to becompiled (translated) and linked or which merely needs to beinterpreted, or an executable software code which merely needs to beloaded into the relevant computer unit for execution.

Lastly, at least one embodiment of the present invention discloses anelectronically readable data medium, e.g. a DVD, a magnetic tape or aUSB stick, on which is stored electronically readable controlinformation, in particular software (see above). When this controlinformation (software) is read from the data medium and stored in acontrol or computer unit of a combined MR/ET facility, all of theinventive embodiments of the above described methods can be performed.

In summary, at least one embodiment of the inventive idea resides inutilizing the geometric information from devices that provide ageometrically correct representation, e.g. PET, for the purpose ofcorrecting MR image data, this being possible as a result of the precisespatial assignment between the devices (e.g. PET and MR) since bothrepresent the same volume section. In this case, the correction of theMR image data can be image-based or raw data-based. The image-basedcorrection can be effected firstly by means of a retrospectiveregistration of the MR image with the PET image, wherein the PET imageis used as a true-to-original reference for registration onto the MRimage, the registration being non-rigid in particular. Secondly, theimage-based correction can be effected by way of an adaptation of thewarp correction using the geometric information that is obtained fromthe PET image. In the case of raw data-based correction, the geometricinformation that is obtained from the PET image can be used during theMR reconstruction or to correct the MR raw data (e.g. in the form of aphase correction).

At least one embodiment of the present invention is suitable for e.g.correlation studies (a combination of fMRI (functional MR imaging) anddynamic PET), for radiotherapy planning, for operation planning and alsofor MR-aided biopsy. Moreover, the present invention allows the accuracyof MR images to be improved, such that e.g. an exact volumetricevaluation can also be performed on the basis of the MR images that arecreated according to at least one embodiment of the invention.Embodiments of the present invention are obviously not restricted tothese preferred fields of application, since the present invention canalso be used generally to improve the geometric accuracy of MR images,thereby allowing greater location integrity of the MR images.

FIG. 1 shows a schematic illustration of a combined MR/PET facility 5,which comprises a positron emission detector 30 and a magnetic resonanceinstallation 24. In this case, a basic field magnet 1 of the magneticresonance installation 24 generates a temporally constant strongmagnetic field in order to polarize or align the nuclear spin in anexamination region of an object O, such as e.g. a part to be examined ina human body which is lying on a table 23 and is pushed into themagnetic resonance installation 24 for the purpose of creating an image.The nuclear spin resonance measurement requires a high level ofhomogeneity of the basic magnetic field, and said homogeneity is definedin a typically spherical measured volume M, in which those parts of thehuman body that are to be examined are arranged for the purpose ofcapturing the MR data. In order to meet the homogeneity requirements andin particular to eliminate temporally invariable influences, so-calledshim plates of ferromagnetic material are attached at suitablelocations. Temporally variable influences are eliminated by means ofshim coils 2.

A cylindrical gradient coil system 3 including three partial windings isused in the basic field magnet 1. Each partial winding is supplied, byway of an amplifier, with current for generating a linear (andtemporally variable) gradient field in the relevant direction of theCartesian system of coordinates. In this case, the first partial windingof the gradient field system 3 generates a gradient Gx in anx-direction, the second partial winding generates a gradient Gy in ay-direction and the third partial winding generates a gradient Gz in az-direction. The amplifier comprises a digital-analog converter, whichis activated by a sequence control 18 for generating gradient pulses atthe correct time.

The gradient field system 3 contains one or more high-frequency antennas4, which convert the high-frequency pulses that are emitted by ahigh-frequency power amplifier into a magnetic alternating field inorder to excite the nuclei and align the nuclear spins of the object O,or the region thereof, that is to be examined. Each high-frequencyantenna 4 consists of one or more HF transmit coils and one or more HFreceive coils in the form of an annular, preferably linear ormatrix-type arrangement of component coils. The HF receive coils of thehigh-frequency antenna 4 are also used to convert the alternating fieldthat is produced by the precessing nuclear spins, i.e. usually thenuclear spin echo signals that are produced by a pulse signal from oneor more high-frequency pulses and one or more gradient pulses, into avoltage (measurement signal) that is supplied via an amplifier 7 to ahigh-frequency receive channel 8 of a high-frequency system 22. Thehigh-frequency system 22 further comprises a transmit channel 9 in whichthe high-frequency pulses for exciting the magnetic nuclear resonanceare generated. In this case, the respective high-frequency pulses arerepresented digitally as a sequence of complex numbers in the sequencecontrol 18 as a result of a pulse sequence that is specified by theinstallation computer 20. This number sequence is supplied as a realpart and an imaginary part via an input 12 in each case to adigital-analog converter in the high-frequency system 22 and thence to atransmit channel 9. In the transmit channel 9, the pulse sequences aremodulated onto a high-frequency carrier signal, whose basic frequencycorresponds to the resonance frequency of the nuclear spin in themeasured volume.

The changeover from transmit mode to receive mode is effected by way ofa transmit-receive filter 6. The HF transmit coils of the high-frequencyantenna(s) 4 beam the high-frequency pulses for exciting the nuclearspin into the measured volume M, and resulting echo signals are sampledvia the HF receive coil(s). The correspondingly obtained nuclearresonance signals are demodulated in a phase-sensitive manner onto anintermediary frequency (wherein e.g. correction parameters can beapplied) in the receive channel 8′ (first demodulator) of thehigh-frequency system 22, and digitized in the analog-digital converter(ADC). This signal is then demodulated onto the frequency 0. Thedemodulation onto the frequency 0 and the separation into a real partand an imaginary part takes place in a second demodulator 8 afterdigitization in the digital domain. An MR image (wherein correctionparameters can likewise be applied) and a PET image (see below) arereconstructed by an image computer 17 from the measured data that isobtained thus. The measured data, the image data and the controlprograms are managed by the installation computer 20. On the basis ofspecifications from control programs, the sequence control 18 monitorsthe generation of the relevant desired pulse sequences and thecorresponding sampling of the k-space. In particular, the sequencecontrol 18 controls the timely switching of the gradients, the emissionof the high-frequency pulses with defined phase amplitude, and thereceipt of the nuclear resonance signals in this case. The time base forthe high-frequency system 22 and the sequence control 18 is provided bya synthesizer 19.

As explained above, the MR/PET facility 5 comprises a positron emissiondetector 30, which is usually of annular design. The tracers that areused in the case of PET are marked by a positron source. When thispositron source decays in the tissue of the patient O, two γ-quantumsare generated by annihilation in the vicinity of the location of thecorresponding positron emission, and fly apart in opposite directions.If these two γ-quantums are measured by two opposing detector elementsof the positron emission detector 30 within a predefined coincidencetime period, the location of the annihilation can be established at aposition on the connection line between said two detector elements.

The positron emission detector 30 is used to capture the PET data fromwhich the PET image is then generated in the image computer 17.According to an embodiment of the invention, the PET image is comparedwith the MR image in the image computer 17, in order to createcorresponding results of this comparison and adapt the MR image to thePET image.

The selection of corresponding control programs for generating the MRimages and PET images, for comparing and correcting the MR images or theabove cited correction parameters, which are stored e.g. on a DVD 21,and the depiction of the generated MR images is coordinated via aterminal 13 comprising a keyboard 15, a mouse 16 and a display screen14.

FIG. 2 illustrates a flowchart of a first method according to anembodiment of the invention.

While the MR image data is captured in the first step S1, PET image datais simultaneously captured by way of a PET detector in the second stepS2. The MR image data is compared with the PET image data in thefollowing step S3. This comparison includes determining a transformationby which the MR image data can be migrated into the PET image data.However, this comparison can also include adapting a warp correction(based on the geometric information of the PET image data), wherein theMR image data can be corrected correspondingly by way of the warpcorrection in order to correspond to the PET image data in terms ofgeometric accuracy.

In the final step S4, the MR image data is corrected depending on theresults of the comparison, such that the MR image data matches the PETimage data as closely as possible. For example, the above-citedtransformation or the above cited warp correction can be applied to theoriginal MR image data for this purpose.

The steps S3 and S4 in FIG. 2 can also be replaced by a registration ofthe MR image data with the PET image data. The PET image is used as atrue-to-original reference for registration of the MR image in thiscase, said registration being non-rigid in particular.

FIG. 3 illustrates a flowchart of a second method according to anembodiment of the invention.

In the first step S11, raw data is captured by means of the magneticresonance installation MR, while PET image data is simultaneouslycaptured by way of the PET detector in the step S12. In the step S13,the phase of the MR raw data is corrected before the MR image data isreconstructed from the MR raw data.

In the following step S14, the MR image data is compared with the PETimage data. This can be realized e.g. by means of a function that takesthe MR image data and the PET image data as an input and outputs ameasure of similarity as an output. If the match between the MR imagedata and the PET image data is insufficiently close in the followingstep S15 (i.e. the measure of similarity is lower than a thresholdvalue), the second method branches to the step S17.

In this step S17, depending on the comparison of the MR image data withthe PET image data in the step S14, the settings of the phase correctionare changed such that better results can be expected in respect of thematch between the MR image data and the PET image data in the nextprogram loop (execution of the steps S13 to S15). If the phasecorrection in the step S3 is effected by way of adding a globallyapplicable phase difference, for example, this phase difference ismodified in the step S17 accordingly.

If the MR image data matches the PET image data sufficiently closely inthe following run (see step S15), the second method branches to the stepS16, in which further MR raw data is captured and is reconstructed byway of the now optimal phase correction to provide MR image data.

The patent claims filed with the application are formulation proposalswithout prejudice for obtaining more extensive patent protection. Theapplicant reserves the right to claim even further combinations offeatures previously disclosed only in the description and/or drawings.

The example embodiment or each example embodiment should not beunderstood as a restriction of the invention. Rather, numerousvariations and modifications are possible in the context of the presentdisclosure, in particular those variants and combinations which can beinferred by the person skilled in the art with regard to achieving theobject for example by combination or modification of individual featuresor elements or method steps that are described in connection with thegeneral or specific part of the description and are contained in theclaims and/or the drawings, and, by way of combinable features, lead toa new subject matter or to new method steps or sequences of methodsteps, including insofar as they concern production, testing andoperating methods.

References back that are used in dependent claims indicate the furtherembodiment of the subject matter of the main claim by way of thefeatures of the respective dependent claim; they should not beunderstood as dispensing with obtaining independent protection of thesubject matter for the combinations of features in the referred-backdependent claims. Furthermore, with regard to interpreting the claims,where a feature is concretized in more specific detail in a subordinateclaim, it should be assumed that such a restriction is not present inthe respective preceding claims.

Since the subject matter of the dependent claims in relation to theprior art on the priority date may form separate and independentinventions, the applicant reserves the right to make them the subjectmatter of independent claims or divisional declarations. They mayfurthermore also contain independent inventions which have aconfiguration that is independent of the subject matters of thepreceding dependent claims.

Further, elements and/or features of different example embodiments maybe combined with each other and/or substituted for each other within thescope of this disclosure and appended claims.

Still further, any one of the above-described and other example featuresof the present invention may be embodied in the form of an apparatus,method, system, computer program, tangible computer readable medium andtangible computer program product. For example, of the aforementionedmethods may be embodied in the form of a system or device, including,but not limited to, any of the structure for performing the methodologyillustrated in the drawings.

Even further, any of the aforementioned methods may be embodied in theform of a program. The program may be stored on a tangible computerreadable medium and is adapted to perform any one of the aforementionedmethods when run on a computer device (a device including a processor).Thus, the tangible storage medium or tangible computer readable medium,is adapted to store information and is adapted to interact with a dataprocessing facility or computer device to execute the program of any ofthe above mentioned embodiments and/or to perform the method of any ofthe above mentioned embodiments.

The tangible computer readable medium or tangible storage medium may bea built-in medium installed inside a computer device main body or aremovable tangible medium arranged so that it can be separated from thecomputer device main body. Examples of the built-in tangible mediuminclude, but are not limited to, rewriteable non-volatile memories, suchas ROMs and flash memories, and hard disks. Examples of the removabletangible medium include, but are not limited to, optical storage mediasuch as CD-ROMs and DVDs; magneto-optical storage media, such as MOs;magnetism storage media, including but not limited to floppy disks(trademark), cassette tapes, and removable hard disks; media with abuilt-in rewriteable non-volatile memory, including but not limited tomemory cards; and media with a built-in ROM, including but not limitedto ROM cassettes; etc. Furthermore, various information regarding storedimages, for example, property information, may be stored in any otherform, or it may be provided in other ways.

Example embodiments being thus described, it will be obvious that thesame may be varied in many ways. Such variations are not to be regardedas a departure from the spirit and scope of the present invention, andall such modifications as would be obvious to one skilled in the art areintended to be included within the scope of the following claims.

1. A method for capturing MR image data by way of a magnetic resonanceinstallation, comprising: capturing the MR image data relating to avolume section of an examination object; capturing image data of thevolume section by way of a true-to-original tomographic method;comparing the MR image data with the image data; and correcting the MRimage data depending on at least one result of the comparison, such thatthe corrected MR image data will match the image data as closely aspossible.
 2. A method for capturing MR image data by way of a magneticresonance installation, comprising: capturing the MR image data relatingto a volume section of an examination object, wherein parameters areused during the capturing of the MR image data; capturing image data ofthe volume section by way of a true-to-original tomographic method;comparing the MR image data with the image data; modifying theparameters depending on at least one result of the comparison, such thatafter the MR image data of the volume section is captured again usingthe modified parameters, the MR image data captured again will match theimage data as closely as possible; and capturing the MR image data ofthe volume section again using the modified parameters.
 3. The method asclaimed in claim 2, wherein a warp correction is used during thecapturing of the MR image data, wherein the parameters are parameters ofthe warp correction, and wherein the parameters are modified dependingon the comparison, and therefore the MR image data is modified by way ofthe warp correction using the modified parameters, such that themodified MR image data matches the image data as closely as possible. 4.The method as claimed in claim 2, wherein MR raw data is captured duringthe capturing of the MR image data, wherein the MR image data isreconstructed from the MR raw data, wherein the parameters areparameters which are applied during the reconstruction of the MR imagedata, and wherein the parameters are modified depending on thecomparison in such a way that, when the MR image data is reconstructedagain from the MR raw data using the modified parameters, thereconstructed MR image data matches the image data as closely aspossible.
 5. The method as claimed in claim 4, wherein the parameterscomprise a phase difference by which a phase of the MR raw data iscorrected.
 6. The method as claimed in claim 5, wherein the phasedifference is specified as an individual phase difference per k-spacepoint, or wherein the phase difference is specified globally as the samephase difference for all k-space points.
 7. The method as claimed inclaim 1, wherein the comparison is part of a non-rigid registration thatis used to create a transformation by which the MR image data aremigrateable into the image data.
 8. The method as claimed in claim 1,wherein the true-to-original tomographic method is a positron emissiontomography.
 9. The method as claimed in claim 1, wherein the capture ofthe MR image data and the capture of the image data take placesimultaneously.
 10. The method as claimed in claim 1, wherein thecomparison is done with reference to anatomical features of theexamination object, the anatomical features being visible to both themagnetic resonance installation and the true-to-original tomographicmethod, or wherein the comparison is done with reference to markerswhich are visible to both the magnetic resonance installation and thetrue-to-original tomographic method.
 11. A combined MR/ET facility forcapturing MR image data of a volume section of an examination object,the MR/ET facility comprising: a control unit configured to activate anemission detector of the MR/ET facility and configured to activate amagnetic resonance installation of the MR/ET facility; and an imagecomputing unit configured to receive raw data of the volume section, theraw data being captured by the emission detector; configured to receiveMR raw data of the volume section, the MR raw data being recorded by themagnetic resonance installation; and configured to create the MR imagedata from the MR raw data and image data from the ET data, wherein theemission detector is so configured as to capture true-to-originaltomographic raw data, wherein the MR/ET facility is so configured as tocompare the MR image data with the image data, and wherein the MR/ETfacility is so configured as to correct the MR image data depending onat least one result of the comparison, such that the MR image data willmatch the image data as closely as possible.
 12. A combined MR/ETfacility for capturing MR image data of a volume section of anexamination object, the MR/ET facility comprising: a control unitconfigured to activate an emission detector of the MR/ET facility andconfigured to activate a magnetic resonance installation of the MR/ETfacility; and an image computing unit configured to capture image databy way of the emission detector or configured to capture MR image databy way of the magnetic resonance installation depending on parameters,wherein the emission detector is so configured as to capturetrue-to-original tomographic image data, wherein the MR/ET facility isso configured as to compare the MR image data with the image data,wherein the MR/ET facility is so configured that, depending on at leastone result of the comparison, the MR/ET facility is configured to modifythe parameters in such a way that, after the MR image data of the volumesection is captured again using the modified parameters, the captured MRimage data captured again will match the image data as closely aspossible.
 13. The combined MR/ET facility as claimed in claim 11,wherein the combined MR/ET facility is a combined MR/PET facility. 14.The combined MR/ET facility as claimed in claim 11, wherein the combinedMR/ET facility is so configured as to carry out capturing the MR imagedata relating to a volume section of an examination object; capturingimage data of the volume section by way of a true-to-originaltomographic method; comparing the MR image data with the image data; andcorrecting the MR image data depending on at least one result of thecomparison, such that the corrected MR image data will match the imagedata as closely as possible.
 15. A computer program product whichcomprises a program and is loadable directly into a memory of aprogrammable control unit of a combined MR/ET facility, includingprogram segments for executing all of the steps of the method as claimedin claim 1 when the program is executed in a control unit of thecombined MR/ET facility.
 16. An electronically readable data medium onwhich is stored electronically readable control information that is soconfigured as to carry out the method as claimed in claim 1 whenexecuted when the data medium is used in a control unit of a combinedMR/ET facility.
 17. The method as claimed in claim 3, wherein MR rawdata is captured during the capturing of the MR image data, wherein theMR image data is reconstructed from the MR raw data, wherein theparameters are parameters which are applied during the reconstruction ofthe MR image data, and wherein the parameters are modified depending onthe comparison in such a way that, when the MR image data isreconstructed again from the MR raw data using the modified parameters,the reconstructed MR image data matches the image data as closely aspossible.
 18. The method as claimed in claim 3, wherein the parameterscomprise a phase difference by which a phase of the MR raw data iscorrected.
 19. The method as claimed in claim 18, wherein the phasedifference is specified as an individual phase difference per k-spacepoint, or wherein the phase difference is specified globally as the samephase difference for all k-space points.
 20. The method as claimed inclaim 2, wherein the comparison is part of a non-rigid registration thatis used to create a transformation by which the MR image data aremigrateable into the image data.
 21. The method as claimed in claim 2,wherein the true-to-original tomographic method is a positron emissiontomography.
 22. The method as claimed in claim 2, wherein the capture ofthe MR image data and the capture of the image data take placesimultaneously.
 23. The method as claimed in claim 2, wherein thecomparison is done with reference to anatomical features of theexamination object, the anatomical features being visible to both themagnetic resonance installation and the true-to-original tomographicmethod, or wherein the comparison is done with reference to markerswhich are visible to both the magnetic resonance installation and thetrue-to-original tomographic method.
 24. The combined MR/ET facility asclaimed in claim 12, wherein the combined MR/ET facility is a combinedMR/PET facility.
 25. The combined MR/ET facility as claimed in claim 12,wherein the combined MR/ET facility is so configured as to carry outcapturing the MR image data relating to a volume section of anexamination object, wherein parameters are used during the capturing ofthe MR image data; capturing image data of the volume section by way ofa true-to-original tomographic method; comparing the MR image data withthe image data; modifying the parameters depending on at least oneresult of the comparison, such that after the MR image data of thevolume section is captured again using the modified parameters, the MRimage data captured again will match the image data as closely aspossible; and capturing the MR image data of the volume section againusing the modified parameters.
 26. A computer program product whichcomprises a program and is loadable directly into a memory of aprogrammable control unit of a combined MR/ET facility, includingprogram segments for executing all of the steps of the method as claimedin claim 2 when the program is executed in a control unit of thecombined MR/ET facility.
 27. An electronically readable data medium onwhich is stored electronically readable control information that is soconfigured as to carry out the method as claimed in claim 2 whenexecuted when the data medium is used in a control unit of a combinedMR/ET facility.
 28. A computer readable medium including programsegments for, when executed on a computer device, causing the computerdevice to implement the method of claim
 1. 29. A computer readablemedium including program segments for, when executed on a computerdevice, causing the computer device to implement the method of claim 2.